The present invention relates to an espresso machine, particularly a steam pressure espresso machine which has a filter holder in which there is a filter strainer and which, with the help of a handle, can be detachably locked to the housing of the espresso machine by way of a bayonet coupling or the like.
In known espresso machines, a filter strainer sits in a filter holder which is provided with a handle and is connected to the espresso machine by way of a bayonet coupling. For placing ground coffee into and removing it from the filter holder, the filter holder is separated from the espresso machine. Under operating conditions, this filter strainer/filter holder unit is under a water pressure of 2-15 bar--depending on the type of machine; this water pressure presses hot water through the ground coffee disposed in the filter strainer. To ensure proper operation, the ground coffee is placed into and removed from the filter strainer so long as the espresso machine is still--or is again--unpressurized. See, for example, DE-C-457,865, FR-A-706,126 or CH-A-162,960.
If, in espresso machines of the above type, the filter holder is separated from the espresso machine under operating pressure, the hot water which would then escape under high pressure may scald the operator or the water pressure may catapult away the filter holder and cause injuries and/or damage to the machine or other property.
In pump espresso machines, which work with operating pressures exceeding 5 bar, it is hardly possible to separate the filter holder from the espresso machine under pressure because the pressing caused by the high pressure between the connecting elements of filter holder and espresso machine is so great that the bayonet catch practically cannot be released. Furthermore, the force-coupled water pump is switched off after the brewing process is completed and, thus, the water pressure is reduced immediately.
In steam pressure espresso machines, on the other hand, which work with pressures of 2-4 bar, safety precautions must be taken to reliably prevent the filter holder from separating from the espresso machine under operating pressure since, in these systems, the steam water pressure is maintained even after the drawing of the coffee is finished.